The 40-year-old Australian appeared at the High Court in London seeking to overturn a lower court's rejection in February of defence arguments that he would have an unfair trial in Sweden.

He is accused of molestation, and what Sweden describes as "minor rape".

Mr Assange's lawyers have criticised Sweden's bid to extradite him over rape allegations as legally flawed.

Lawyer Ben Emmerson has described the extradition bid as somewhat of a fishing expedition - Sweden's grab at a chance to question Mr Assange - and not for the purpose of prosecution.

He said the conduct described in the European arrest warrant issued by Sweden "fails to provide a fair, proper and accurate description of what is alleged against the appellant".

After the ruling against him in February, Mr Assange blasted the decision as "a result of the European Arrest Warrant system run amok".

Mr Emmerson also argued that Mr Assange was a victim of a "philosophical and judicial mismatch" between English and Swedish law, saying some of the allegations levelled against him would not amount to sex crimes in Britain.

Swedish authorities want to question Mr Assange over the sex assault claims made by two women - allegations he denies - although he has not been formally charged.

He has claimed the allegations are politically motivated and linked to his whistleblower website's releases of huge caches of leaked US government documents, which have infuriated Washington.

At Tuesday's hearing, Mr Emmerson highlighted that one of the allegations on the warrant is of rape - that a woman he was in bed with woke up to find Mr Assange having unprotected sex with her.

But Mr Emmerson said once she discovered the situation, the woman consented, and the offence would not amount to rape in Britain.

"We say what the authorities establish is that the offence, the circumstances as described, must be reasonably recognised as being rape in the United Kingdom," he said.

The alleged incident "does not constitute the offence of rape as recognised in the UK," he added.

Mr Assange shook up his legal team before the trial, splitting with media lawyer Mark Stephens and taking on Gareth Peirce, a high-profile human rights lawyer.

Under the British system, Mr Peirce directs the legal team but another lawyer - in this case Mr Emmerson - is given the job of presenting the case in court.

The new team seemed to herald a fresh approach. After previous hearings, Mr Assange made lengthy defiant statements to the scrum of journalists waiting outside court.

But on Tuesday (local time), the former computer hacker, dressed smartly in a grey suit, white shirt, blue tie and reading glasses, refused to say a word as he walked past the waiting microphones.

A group of some 20 supporters waited outside the court, one of whom shouted "Keep fighting the American empire, Julian" as Mr Assange arrived. Other backers at the court included campaigning journalist John Pilger.

Mr Assange has said his greatest fear was eventual extradition to the United States, where his lawyers argued he could be sent to the Guantanamo Bay detention facility or face the death penalty.

Mr Assange has been living under strict bail conditions, including wearing an electronic ankle tag and a curfew, at a friend's mansion in eastern England since December.

The hearing on Tuesday and Wednesday is taking place before two judges. A decision is expected to be deferred until a later date.

But Mr Assange's Swedish lawyer, Bjorn Hurtig, said on Tuesday there was a "big risk" the court will decide to extradite his client.

Mr Assange's lawyers have signalled he is prepared for a lengthy legal battle and could take his challenge all the way to the Supreme Court, although that can only be done on a point of law considered in the wider public interest.

He was arrested in December over the sex assault claims, as his whistleblowing website was in the process of releasing a huge cache of leaked US diplomatic cables.

US authorities opened a criminal investigation against Assange in July 2010 but are yet to bring any charges against him.